Process for the preparation of alkoxyalkanoic acids

ABSTRACT

A process for the preparation of an alkoxyalkanoic acid by reacting the corresponding alkoxyalkanol with a stable free radical nitroxide in the presence of a cerium salt, a highly polar solvent, an oxidant and water, at a temperature in the range of from about 0° C. to about 100° C. and thereafter separating out the alkoxyalkanoic acid.

FIELD OF THE INVENTION

This invention relates to a process for the preparation ofalkoxyalkanoic acids by the oxidation of the correspondingalkoxyalkanols in the presence of a stable free radical nitroxide, acerium salt, a nitrite compound, a highly polar solvent, an oxidant andwater.

BACKGROUND OF THE INVENTION

Alkoxyalkanoic acids are useful as anionic detergents and emulsifyingagents. These acids, being composed of only the elements C, H and O, donot pose the environmental problems that other detergents containingheteroatoms such as N, S and P pose. Commercially, the alkoxyalkanoicacids are prepared in a two-step process of first reacting analkoxyalkanol with sodium and then reacting the resultant alkoxide withthe sodium salt of chloroacetic acid.

It is also known to convert alkoxyalkanols such as methyl carbitol tothe corresponding carboxylic acids by oxidizing them with nitric acid.However, not all of the nitric acid can be separated by distillation,and the reaction product contains nitric acid, which is corrosive andtherefore undesirable. In addition, cleavage of the ether linkagesoccurs to a large degree during this process.

Japanese Patent No. 50-96519 issued on Jul. 31, 1975, discloses aprocess for the preparation of carboxylic acid salts by the liquid phasedehydrogenation of alcohols with caustic alkali in the presence ofprecious metal catalysts, including palladium. This process uses arelatively high temperature, 100° C.-270° C. These high temperatures candegrade the ether linkages, especially in the highly ethoxylatedalcohols.

It is known to use nitroxyl radicals/oxoammonium salts in the oxidationof primary alcohols to produce aldehydes and acids and secondaryalcohols to ketones (Journal of Organic Chemistry, Vol. 52 (12), pp.2559-2562, and Journal of Organic Chemistry, Vol. 55, 1990, pp.462-466).

It is also reported in the open literature that primary aliphaticalcohols can be converted to aldehydes in 30-40% yields in the presenceof catalytic amounts of cuprous chloride,2,2,6,6,-tetramethylpiperidine-l-oxyl, and atmospheric oxygen (Journalof American Chemical Society, 1984, 106, pp. 3374). It is also knownthat higher yields of aldehydes can be obtained if stoichiometricamounts of cupric or ferric salts are used instead of catalytic amountsof the cuprous salts (Pure and Applied Chemistry, vol. 62(2), 1990, pp.217-222).

It is generally more difficult to oxidize alkoxyalkanols than alkanolsas it is difficult to oxidize alkoxyalkanols without splitting themolecular chain at the ether linkage and thereby produce a largeproportion of undesired by-product.

It has been found that alkoxyalkanoic acids can be produced in goodyields from alkoxyalkanols without producing large amounts of highlycorrosive, difficult to separate, by-products. This can be accomplishedby using catalytic amounts of a stable free radical nitroxide, a ceriumsalt which is at least partially soluble, a nitrite compound, a highlypolar solvent, and an oxidant.

SUMMARY OF THE INVENTION

This invention relates to a process for the preparation of analkoxyalkanoic acid of the formula RO(CH₂ CHR'O)_(n) CH₂ CO₂ H wherein Ris an alkyl group of from about 1 to about 22 carbon atoms, R' ishydrogen or alkyl or mixtures thereof (on the individual molecule) and nis an integer of from about 1 to about 500 which comprises reacting thecorresponding alkoxyalkanol with a stable free radical nitroxide havingthe formula: ##STR1## wherein (1) (a) each of R₁, R₂, R₃ and R₄ is analkyl, aryl or substituted alkyl group having 1 to about 15 carbonatoms, and (b) R₅ and R₆ (i) each is an alkyl group having 1 to about 15carbon atoms provided that R₁ -R₆, are not all alkyl groups, or asubstituted alkyl group having 1 to about 15 carbon atoms wherein thesubstituent is hydrogen, cyano, --CONH₂, --OCOCH, OCOC₂ H₅, carbonyl,alkenyl wherein the double bond is not conjugated with the nitroxidemoiety, or --COOR wherein R of the --COOR group is alkyl or aryl, or(ii) together form part of a ring that contains at least 3 carbon atomsand up to two heteroatoms of O or N, or (2) the ##STR2## moiety and the##STR3## moiety individually are aryl, or (3) the ##STR4## moiety andthe ##STR5## moiety together form a bicyclic ring with the proviso thatthe group directly adjacent to the N--O moiety is a bridgehead C--H, ora fully alkylated carbon, in the presence of a cerium salt which is atleast partially soluble, a nitrite compound, a highly polar solvent, anoxidant and water, at a temperature in the range of from about 0° C. toabout 100° C. and thereafter separating out the alkoxyalkanoic acid.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present process converts alkoxyalkanols of the formula RO(CH₂CHR'O)_(n) CH₂ CH₂ OH (I) wherein R is an alkyl group having from about1 to about 22 carbon atoms, preferably from about 11 to about 18 carbonatoms, R' is hydrogen or alkyl or mixtures thereof (on the individualmolecule) and n represents the average number of oxyalkylene groups andis an integer of from about 1 to about 500, preferably from about 1 toabout 50, more preferably 1 to about 12, and most preferably from about2 to about 9, to the corresponding alkoxyalkanoic acids of the formulaRO(CH₂ CHR'O)_(n) CH₂ CO₂ H (II) by contacting the alkoxyalkanol with astable free radical nitroxide in the presence of a cerium salt, anitrite compound, a highly polar solvent, an oxidant and water, at atemperature in the range of from about 0° C. to about 100° C. andthereafter separating out the alkoxyalkanoic acid. The R group in theabove formula I can be substituted with any substituent which does notinterfere with the oxidation of the hydroxy group. Such substituentsinclude --OR", --CH₃, --COOH, CONH₂ and COOR" wherein R' is an alkyl oraryl group. The process of the instant invention is particularly suitedto detergent range ethoxylated, or propoxylated alcohols with alkylchains (R) of about 8 to about 20, preferably about 11 to about 18carbon atoms. The R' groups on an individual molecule can be hydrogen,alkyl, or mixtures thereof. For example, straight ethoxylated, straightpropoxylated and mixed ethoxylated-propoxylated detergent alcohols arecommercially available. The number of such alkoxylate groups, CH₂ CHR'O,ranges from about 1 to about 500. Commercially, detergent rangeethoxylate alcohols are available with an average of 3, 7, 9 and 12ethoxylate units per molecule. Others can be readily prepared. In apreferred embodiment, the alkoxyalkanol reactant is an ethoxylatedalcohol which has had the unreacted alcohols and lower ethoxylatestopped off in order to give an ethoxylate product having less than about5 percent by weight of the starting alkanol.

The term "stable free radical nitroxide" as used herein shall mean afree radical nitroxide that can be prepared by conventional chemicalmethods and will exist long enough to be used in a subsequent chemicalreaction or examined in a static system by normal methods ofspectroscopy. Generally, the stable free radical nitroxides of thepresent invention have a half life of at least one year. The term"stable free radical" shall also be understood to include the precursorto a stable free radical from which the stable free radical may beproduced in situ.

The stable free radical nitroxides, as used in the present process, areprecursors to catalysts, i.e., oxoammonium salts, active for theoxidation of alkoxyalkanols to the corresponding acids. These catalystsare generated in situ by the oxidation of a stable free radicalnitroxide to an oxoammonium salt. The stable free radical nitroxide canbe obtained by the oxidation of amines or hydroxylamines.

The stable free radical nitroxides which are suitable for use in theinstant invention have the formula: ##STR6## wherein each of R₁, R₂, R₃and R₄ is an alkyl, aryl or substituted alkyl groups and no hydrogen isbound to the remaining valences on the carbon atoms bound to thenitrogen. As used herein, the term "alkyl" is meant to includecycloalkyl. The alkyl (or substituted) groups R₁ -R₄ may be the same ordifferent, and preferably contain 1 to 15 carbon atoms. Preferably, R₁-R₄ are methyl, ethyl, or propyl groups. In addition to hydrogen, thesubstituents may include, halogen, oxygen, nitrogen and the like.

The remaining valences (R₅ and R₆) in formula III above may be satisfiedby any atom or group except hydrogen which can bond covalently tocarbon, although some groups may reduce the stabilizing power of thenitroxide and are undesirable. When R₁, R₂, R₃ and R₄ are each alkylgroups, however, at least one of R₅ and R₆ must be an aryl group.Preferably, R₅ and R₆ are substituted alkyl groups having 1 to about 15carbon atoms wherein the substituent is selected from halogen, cyano,--COOR, wherein R is alkyl or aryl, --CONH₂, --OCOC₂ H₅, carbonyl, oralkenyl where the double bond is not conjugated with the nitroxidemoiety, or alkyl groups of 1 to about 15 carbon atoms.

The remaining valences (R₅ and R₆) in formula III above may also form aring containing at least three carbon atoms and up to two heteroatoms,such as O or N. R₅ and R₆ can, for example, form a five-membered ringcontaining 3 carbon atoms and up to two heteroatoms, such as O or N, afive-membered ring containing 4 carbon atoms, a six-membered ringcontaining 5 carbon atoms, a seven-membered ring containing 6 carbonatoms, an eight-membered ring containing 7 carbon atoms, etc. Forpurposes of this invention, it is preferred that R₅ and R₆ together forma five-membered ring, a six-membered ring, a seven-membered ring, or aneight-membered ring, although larger rings would also be suitable.Examples of suitable compounds having the structure above and in whichR₅ and R₆ form part of the ring are2,2,6,6,-tetramethylpiperidine-1-oxyl,2,2,5,5-tetramethylpyrrolidin-1-oxyl,2,2,7,7-tetramethylcycloheptan-1-oxyl, mixtures thereof, and the like.It is understood that these compounds may contain substituents which donot interfere with the reaction.

The ##STR7## moieties in formula III above can individually be aryl,i.e., ##STR8## Examples of suitable compounds having the structure abovein which the ##STR9## moleties are individually aryl arediphenylamine-N-oxyl, phenyl tertiary butylamine-N-oxyl,3-methyl-diphenylamine-N-oxyl, 2-chlorophenylamine-N-oxyl and the like.These compounds may be substituted with an substituents which do notinterfere with the reaction.

The ##STR10## moieties in formula III above can also form a bicyclicring wherein the group adjacent to the N-O moiety is either a bridgeheadC--H or a quaternary carbon. As used herein, the term "bridgehead C--H"refers to a tertiary carbon which is common to both rings of thebicyclic ring system. As used herein, "a quaternary carbon" refers to afully substituted carbon atom having alkyl, aryl or substituted alkylgroups having 1 to about 18 carbon atoms as substituents. Examples ofsuitable compounds having the structure above in which the ##STR11##moieties form a bicyclic ring are 2-azabicyclo-[2.2.1 ]heptan-2-oxyl,2-azabicyclo[2.2.2]-3,3-dimethyloctan-2-oxyl,3-azabicyclo[3.2.2]-2,2,4,4-tetramethylnonan-3-oxyl and the like. Thesecompounds may be substituted with any substituents which do notinterfere with the reaction.

In a preferred embodiment, the stable free radical nitroxide is apiperidine-1-oxyl having the formula: ##STR12## wherein each of R₇, R₈,R₉ and R₁₀ is an alkyl, aryl or substituted alkyl group having 1 toabout 15 carbon atoms and no hydrogen is bound to the remaining valenceson the carbon atoms bound to the nitrogen, and each of R₁₁ and R₁₂ isalkyl, hydrogen, aryl or a substituted heteroatom. As used herein, theterm "alkyl" is meant to include cycloalkyl. The alkyl (or substituted)groups R₇ -R₁₀ may be the same or different, and preferably contain 1 to15 carbon atoms. Preferably, R₇ -R₁₀ are methyl, ethyl, or propylgroups. In addition to hydrogen, the substituents may include, halogen,oxygen, nitrogen and the like. Typically, one of R₁₁ and R₁₂ ishydrogen, with the other one being a substituted heteroatom which doesnot interfere with the reaction. Suitable substituted heteroatomsinclude --OR, ##STR13## --N⁺ Me₃ Cl--, --O--SO₃ H, --O--polymer and thelike.

In a particularly preferred embodiment, the nitroxide is selected fromthe group consisting of 2,2,6,6-tetramethylpiperidine-1-oxyl,4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl,2,2,6,6-tetramethylpiperidine-1-oxyl-4-sulfate,4-methoxy-2,2,6,6-tetramethylpiperidine-1-oxyl,4-ethoxy-2,2,6,6-tetramethylpiperidine-1-oxyl,4-carbamoyl-2,2,6,6-tetramethylpiperidine-1-oxyl,4-acetylamino-2,2,6,6-tetramethylpiperidine-1-oxyl,4-benzoylamino-2,2,6,6-tetramethylpiperidine-1-oxyl,4-pivaloylamido-2,2,6,6-tetramethylpiperidine-1-oxyl,4-dodecyloylamido-2,2,6,6-tetramethylpiperidine-1-oxyl,4-dodecanoylamino-2,2,6,6-tetramethylpiperidine-1-oxyl,4-octanoylamino-2,2,6,6-tetramethylpiperidine-1-oxyl and mixturesthereof, with 2,2,6,6-tetramethylpiperidine-1-oxyl,4-acetylamino-2,2,6,6-tetramethylpiperidine-1-oxyl, and4-methoxy-2,2,6,6-tetramethylpiperidine-1-oxyl being especiallypreferred.

The cerium salt, in conjunction with nitrite in the present process isbelieved to effect oxidation of the free radical nitroxide to thecatalytically active oxoammonium ion. The salt will typically be ahalide salt such as a chloride salt, a bromide salt, a nitrate salt, ora fluoride salt, as well as any other cerium salt which is at leastpartially soluble in the reaction solution. In a preferred embodimentthe salt is selected from the group consisting of cerium chloride,cerium bromide, cerium fluoride, cerium nitrate and mixtures thereof.The amount of cerium salt utilized in the present process is typicallyfrom about 0.1 mole percent to about 100 mole percent, preferably fromabout 10 mole percent to about 20 mole percent, basis the startingalkoxyalkanol.

The nitrite compound in the present process is typically selected fromthe group consisting of sodium nitrite, potassium nitrite and mixturesthereof, with sodium nitrite being preferred. However, any compoundwhich serves to generate nitrite ion during the course of the reactionand which does not interfere with the reaction would be suitable. Theamount of nitrite compound utilized in the present process is typicallyfrom about 5 mole percent to about 500 mole percent, preferably fromabout 25 mole percent to about 75 mole percent, basis the startingalkoxyalkanol.

The reaction of the present invention is carried out in the presence ofa highly polar solvent. The solvent is generally one in which thealkoxyalkanol is readily soluble. Solvents which are most suitable arehighly polar solvents which are inert in the reaction. It is, however,contemplated that the reaction may be carried out in the absence of asolvent or with solvents, other than highly coordinating solvents, suchas, for example, ethers, polyethers and alkyl ethoxycarboxylates in theevent pressures higher than atmospheric pressure and/or reaction timeslonger than about 6 hours are utilized. The solvent may be added to thereaction mixture, or alternatively, the nitroxide may be dissolved inthe solvent prior to addition of the nitroxide to the reaction medium.The solvent is typically selected from the group consisting ofacetonitrile, sulfolane, N-methylpyrrolidinone, acetic acid and mixturesthereof. In a preferred embodiment, the solvent is acetonitrile. Theamount of solvent utilized in the process is typically in the range offrom about 0.5:1 to about 100:1, preferably from about 2:1 to about10:1, basis the weight of the starting alkoxyalkanol.

The process of the present invention is also carried out in the presenceof an oxidant. The oxidants suitable for use in the instant inventionare believed to be those compounds which are capable of oxidizing themetal salts to a form such that they react with the stable free radicalnitroxide to form the oxoammonium salt. Suitable oxidants includeoxygen-containing gases such as pure oxygen and oxygen in air. Whereaspure oxygen can is preferred to accomplish the desired conversion, theoxygen can also be diluted with an inert gas such as nitrogen, helium,argon, or other similar gas. For purposes of increasing the reactionrate, higher O₂ pressures such as, for example, up to about 2000 psigcan be utilized. In a preferred embodiment, pure oxygen is used as theoxidant and it is bubbled into the reaction solution at ambientpressure.

The process of the present invention is also carried out in the presenceof water. The amount of water typically added is in the range of fromabout 10 mole percent to about 1000 mole percent, preferably from about100 mole percent to about 400 mole percent, basis the moles of startingalkoxyalkanol.

The amounts and concentrations of the reactants utilized in the processof the instant invention can vary within wide ranges. The amount ofstable free radical nitroxide is typically in the range of from about0.01 mole percent to about 200 mole percent, preferably from about 5mole percent to about 20 mole percent, basis the number of molesstarting alkoxyalkanol. Generally, the amount of nitrite compound usedis in the range of from about 5 mole percent to about 500 mole percent,basis the number of moles of alkoxyalkanol. The amount of cerium salt istypically in the range of from about 0.1 mole percent to about 100 molepercent, preferably from about 10 mole percent to about 20 mole percent,basis the starting alkoxyalkanol.

The process of the present invention is typically conducted under mildconditions, with good results being obtained using a temperature in therange of from about 0° C. to about 100° C., preferably about 20° C. toabout 70° C., and most preferably, about 35° C. to about 60° C. Reactionpressures are not critical although higher pressures can result inincreased reaction rates. Pressures in the range of from aboutatmospheric pressure up to about 2000 psig can be employed with goodresults.

The process of the instant invention can be carried out either batchwiseor continuously, using a stirrer equipped reactor or other well knowncontacting technique to achieve adequate mixing. Preferred reactionconditions, e.g., temperature, pressure, flow rates, etc., vary somewhatdepending on the specific nitroxide utilized and on the concentration ofthe nitroxide.

The process of the instant invention can be carried out in a variety ofways. For example, 0.03 moles of alkoxyalkanol, and 0.006 moles of thenitroxide, 0.001 moles of cerium salt, and solvent may be added to thereaction vessel, followed by the addition of 0.015 moles of sodiumnitrite and 0.11 moles of water and bubbling oxygen through the reactionmixture. Following the reaction, the product may be separated from thereaction mixture using conventional procedures such as extraction usinga suitable extraction solvent such as, for example, ethyl acetate;evaporation wherein the solvent is stripped from the reaction mixture byusing heat or vacuum.

Depending upon process conditions and the nitroxide used, the yields ofalkoxyalkanoic acid obtained by this invention are typically at leastabout 50%. The products produced by the instant process can be used in avariety of detergent applications and emulsifying agents. For example,these products can be used in light duty dishwashing liquids, shampoos,heavy duty laundry liquids and heavy duty powders.

The ranges and limitations provided in the instant specification andclaims are those which are believed to particularly point out anddistinctly claim the present invention. It is, however, understood thatother ranges and limitations which perform substantially the samefunction in the same or substantially the same manner to obtain the sameor substantially the same result are intended to be within the scope ofthe instant invention as defined by the instant specification andclaims.

The process of this invention will be further described by the followingembodiments which are provided for illustration and are not to beconstrued as limiting the invention.

ILLUSTRATIVE EMBODIMENTS

In the following examples, the starting alkoxyalkanol was aNEODOL®Ethoxylate 23-3T alcohol which was prepared by ethoxylating amixture of C₁₂ and C₁₃ substantially straight chain alcohols (C₁₂ :C₁₃˜40:60) to form an ethoxylate alcohol having about 3 ethylene oxideunits per molecule and then topping off the unreacted alcohols and lowerethoxylates so that the final product has less than about 5 percent byweight of the starting alkanol.

Example 1

12 Grams of NEODOL® Ethoxylate 23-3T, 0.9 grams of2,2,6,6-tetramethylpiperidine-1-oxyl, 0.5 grams of CeCl₃, 1 gram ofsodium nitrite, 2 grams of water, and 25 milliliters of acetonitrilewere charged to a 100 milliliter round bottomed flask. O₂ was bubbledthrough this mixture at a rate of 35 milliliters/minute at ambientpressure. The reaction temperature was held at 45° C. over a 5-hourperiod. The results are presented in Table I.

Comparative Example A

Comparative Example A was carried out in a manner similar to Example 1except that no nitroxide was used. The results are presented in Table I.

Comparative Example B

Comparative Example B was carried out in a manner similar to Example 1except that no nitrite was used. The results are presented in Table I.

Comparative Example C

Comparative Example C. was carried out in a manner similar to Example 1except that 1 gram of sodium nitrate was used in the place of 1 gram ofsodium nitrite. The results are presented in Table I.

Comparative Example D

Comparative Example D was carried out in a manner similar to Example 1except that no cerium salt was used. The results are presented in TableI.

As can be seen in Table I, nitroxide, nitrite, and cerium salt arenecessary for the oxidation of the alkoxyalkanol to proceed.

                  TABLE I    ______________________________________    Oxidation of Alkoxyalkanols to Alkoxyalkanoic acids    % Yield Alkoxyalkanoic Acids    ______________________________________    Example 1           53    Comparative Example A                        0    Comparative Example B                        0    Comparative Example C                        0    Comparative Example D                        0    ______________________________________

What is claimed is:
 1. A process for the preparation of analkoxyalkanoic acid of the formula RO(CH₂ CHR'O)_(n) CH₂ CO₂ H wherein Ris an alkyl group of from about 1 to about 22 carbon atoms, R' ishydrogen or alkyl or mixtures thereof (on the individual molecule) and nis an integer of from about 1 to about 500, which comprises reacting thecorresponding alkoxyalkanol with a stable free radical nitroxide havingthe formula: ##STR14## wherein (1) (a) each of R₁, R₂, R₃ and R₄ is analkyl, aryl or heteroatom substituted alkyl group having 1 to about 15carbon atoms, and (b) R₅ and R₆ (i) each is an alkyl group having 1 toabout 15 carbon atoms provided that R₁ -R₆ are not all alkyl groups, ora substituted alkyl group having 1 to about 15 carbon atoms wherein thesubstituent is hydrogen, cyano, --CONH₂, --OCOCH, OCOC₂ H₅, carbonyl,alkenyl wherein the double bond is not conjugated with the nitroxidemoiety, or --COOR wherein R of the --COOR group is alkyl or aryl, or(ii) together form part of a ring that contains at least 3 carbon atomsand up to two heteroatoms of O or N, (2) the ##STR15## moiety and the##STR16## moiety individually are aryl, or (3) the ##STR17## moiety andthe ##STR18## moiety together form a bicyclic ring with the proviso thatthe group directly adjacent to the N-O moiety is a bridgehead C--H, or afully alkylated carbon, in the presence of a cerium salt which is atleast partially soluble, a nitrite compound, a highly polar solvent, anoxidant and water, at a temperature in the range of from about 0° C. toabout 100° C. and thereafter separating out the alkoxyalkanoic acid. 2.The process of claim 1 wherein said alkoxyalkanol has a carbon number inthe range from about 11 to about
 18. 3. The process of claim 1 whereinthe stable free radical nitroxide is selected from the group consistingof 2,2,6,6,-tetramethylpiperidine-1-oxyl,2,2,5,5-tetramethylpyrrolidin-1-oxyl,2,2,7,7-tetramethylcycloheptan-1-oxyl, and mixtures thereof.
 4. Theprocess of claim 1 wherein the stable free radical nitroxide has theformula: ##STR19## wherein each of R₇, R₈, R₉ and R₁₀ is an alkyl, arylor heteroatom substituted alkyl group having 1 to about 15 carbon atomsand each of R₁₁ and R₁₂ is alkyl, hydrogen, aryl or a substitutedheteroatom.
 5. The process of claim 4 wherein the stable free radicalnitroxide is selected from the group consisting of2,2,6,6-tetramethylpiperidine-1-oxyl,4-methoxy-2,2,6,6-tetramethylpiperidine-1-oxyl,4-ethoxy-2,2,6,6-tetramethylpiperidine-1-oxyl,4-acetylamino-2,2,6,6-tetramethylpiperidine-1-oxyl,4-carbamoyl-2,2,6,6-tetramethylpiperidine-1-oxyl,4-benzoylamino-2,2,6,6-tetra-methylpiperidine-1-oxyl,4-pivaloylamido-2,2,6,6-tetramethylpiperidine-1-oxyl,4-dodecyloylamido-2,2,6,6-tetramethylpiperidine-1-oxyl,4-dodecanoylamino-2,2,6,6-tetramethylpiperidine-1-oxyl,4-octanoylamino-2,2,6,6-tetramethylpiperidine-1-oxyland mixtures thereof.
 6. The process of claim 5 wherein the stable freeradical nitroxide is selected from the group consisting of2,2,6,6-tetramethylpiperidine-1-oxyl,4-acetylamino-2,2,6,6-tetramethylpiperidine-1-oxyl,4-methoxy-2,2,6,6-tetramethylpiperidine-1-oxyl and mixtures thereof. 7.The process of claim 1 wherein said cerium salt is selected from thegroup consisting of cerium chloride, cerium bromide, cerium nitrate,cerium flouride and mixtures thereof.
 8. The process of claim 1 whereinthe solvent is selected from the group of acetonitrile, sulfolane,N-methylpyrrolidinone, acetic acid and mixtures thereof.
 9. The processof claim 8 wherein the solvent is acetonitrile.
 10. The process of claim1 wherein said nitrite compound is selected from the group consisting ofsodium nitrite, potassium nitrite and mixtures thereof.
 11. The processof claim 10 wherein said nitrite compound is sodium nitrite.
 12. Theprocess of claim 1 wherein the amount of nitrite compound is in therange of from about 5 mole percent to about 500 mole percent, basis themoles of starting alkoxyalkanol.
 13. The process of claim 1 wherein saidalkoxyalkanol is contacted with said stable free radical nitroxide andsaid solvent, followed by the addition thereto of said nitrite compoundand said cerium salt.
 14. The process of claim 13 wherein the amount ofstable free radical nitroxide is in the range of from about 0.01 molepercent to about 200 mole percent, basis the number of moles ofalkoxyalkanol.
 15. The process of claim 13 wherein the amount of nitritecompound is in the range of from about 5 mole percent to about 500 molepercent, basis the number of moles of alkoxyalkanol.
 16. The process ofclaim 1 wherein said oxidant is an oxygen-containing gas.
 17. Theprocess of claim 16 wherein said oxygen-containing gas is selected fromthe group consisting of pure oxygen and air.
 18. The process of claim 1wherein the amount of water is in the range of from about 10 molepercent to about 1000 mole percent, basis the moles of startingalkoxyalkanol.
 19. The process of claim 1 wherein said process iscarried out at a temperature in the range of from about 20° C. to about70° C. and at atmospheric pressure.